Cal. Water Code § 46000

A preliminary assessment is an assessment levied by the board of an equal amount upon each acre of land in the district sufficient to pay all warrants issued by the department in accordance with this division, and to defray all other expenses as estimated by the board incurred and to be incurred for the general benefit of the district up to the time of the levy of assessments provided for in Chapter 2 (commencing with Section 46150) of this part, including expenses incurred prior to the organization of the district but in the judgment of the board properly incurred for the general benefit of the district.